How do I set up router for 1 ip address

I have two computers networked at home using Windows XP Home ed. Both have NIC cards in them and I have a Linksys BEFSR41 Router. Is it better to have two IP addresses from my COX cable isp or use 1 ip address for both. I like to play UT with my kids on the computers. If the 1 IP is better How do I set up the 1 ip address for both computers.?

By default, if you setup the workstations to use DHCP for their respective network card properties (as in the manual), they should communicate fine with each other, so you can play your games. The router will get its needed address from your provider. Plus, the router only needs one address (hence the point of using it for most people) to get many machines online.